1. Field of the Invention
The present invention relates to an image decoding apparatus, an image encoding apparatus, a recording medium, a method of transmitting a picture signal, and an image display device, more particularly to improvement of a recording medium such as video tape and video disk, an encoding apparatus for encoding a picture signal which has been recorded on the recording medium, and the decoding apparatus for decoding a picture signal which has been recorded and encoded on the recording medium, and a method of transmitting a picture signal in a digital television broadcasting, a video conference system, or the like, and the image encoding apparatus and the image decoding apparatus in said system, and the image display device of television, etc.
2. Description of the Related Art
Heretofore, in the image decoding apparatus to decode images and the image encoding apparatus to encode images, the image to be displayed on the screen of display device depends on the individual display device For example, in the television (TV) display device, there are many cases where the contrast emphasizing mode to emphasize the contrast is equipped in order to obtain subjectively sharp picture quality. More specifically, as shown in FIG. 1, tones in the low luminance area and high luminance area are compressed (encoded) and tone in the medium luminance area which is viewed by human eye comfortably is enlarged. In the medium luminance area, the contrast between the dark part and the bright part increases and thus the contrast is emphasized and subjectively clear picture quality can be obtained.
However, the degree of compression of tones of output signal in the low luminance area, medium luminance area and high luminance area, ie., the degree of slope in each luminance area of output signal, as shown in FIG. 1, differs according to the type of televisions (TVs). Accordingly, there has been a problem that if the different types of televisions (TVs) were used for the same image, the same image would not be displayed on the display device and the exact image intended by the producer would not be expressed.
Furthermore, in the display device in which contrast emphasizing mode was equipped as described above, if the decoded image deteriorated by the compression (encoding) was displayed, deterioration of picture quality was emphasized and false contours became apparent and thus created a problem. This problem can be solved by displaying the image using the mode in which deterioration of picture quality would not be conspicuous, not using the mode like the contrast emphasizing mode which emphasizes the deterioration of picture quality.
However, in various modes of the display device, there has been no index to judge which mode is the mode that would not highlight the deterioration of picture quality. This applies to the case of controlling various types of parameters (such as picture and sharpness) without setting the mode.